Thermodynamic simulation of the reaction mechanism of Mn2+ oxidation with an SO2/O2 mixture

Manganese oxides are essential in the production of electronic components and batteries. A promising alternative for their production from secondary sources is the leaching of the Mn and later oxidative precipitation of Mn2+ by an SO2/O2 mixture. The steps involved in this last reaction have not been fully understood. This work presents the reaction mechanism describing the oxidative precipitation of Mn2+ by an SO2/O2 mixture with MnO2 and SO42− as reaction products. The analysis was supported in thermodynamic simulations in which the formation and effect of the oxidant species was verified. The proposed reaction mechanism was validated with experimental batch tests and it was found that it describes satisfactorily the oxidation reaction. Experimental evidence revealed that this system is efficient at low concentrations of SO2 in the gas mixture composition; an optimal composition of 7.3% SO2 of the gas mixture was found.